1. Field of the Invention
The present invention relates to an ink, and an ink-applying process and an ink-applying apparatus using this ink.
2. Description of the Background Art
Water-based inks are principally used as inks for ink-jet printers which have become widely used with the spread of computers from the viewpoint of safety and the like. Among these, water-based inks using a water-soluble dye are most widely spread because of their excellent coloring ability. However, the water-based inks using such a water-soluble dye involve problems that they are poor in water fastness because the dye is soluble in water, and that they are rapidly deteriorated by light or gasses such as ozone because the dye is in a molecular state.
In order to solve these problems, an investigation is carried out as to inks using an insoluble coloring agent such as a pigment, which is in such a form that a plurality of molecules are agglomerated, and not in the state of a molecule. These dispersed type inks are superior in the so-called image fastness properties such as water fastness, light fastness and gas fastness compared to inks using water-soluble coloring matter, but are required to be more improved in storage stability and the fixing ability of an image formed.
Thus, in order to enhance the dispersibility of fine particles of an insoluble coloring agent to stabilize ejection and to improve the fixing ability of an image, there have been proposed inks using a block copolymer (see U.S. Pat. No. 5,085,698) and a graft copolymer (see U.S. Pat. No. 5,714,538), which contain a portion easy to adhere to such an insoluble coloring agent and a portion having high affinity for a hydrophilic medium. Further, there has also been proposed a method, in which an oil-soluble dye insoluble in water is dissolved in an organic solvent, the resultant solution is mixed with a polymer, and water is added to this mixture to make the medium hydrophilic, thereby depositing the oil-soluble dye as fine particles (see U.S. AA 20020032252).
According to these techniques, the dispersion stability of the coloring agent is improved by the action of the block copolymer or graft copolymer containing segments having affinity for both the insoluble coloring agent and the hydrophilic medium. However, still more improvements are desired from the viewpoints of lowering the viscosity for stabilizing ejection and improving fixing ability.